"but they do not accept cash. Cash has worked all over the world for hundreds of years, but progress means it is no longer good enough in an increasing number of places.
Totally agree, IT systems can fail anywhere at any time and it can cause complete havoc, take the recent IT outage in the UK airports, it has happened before with several airlines, with check in computers, even ATC systems with their backups have failed. Now of course a restaurant or bar is not going to cause that much trouble, but they should always accept cash as a backup! Just in case!